In sh and bash
touch true
chmod +x true
./true
echo $?
prints 0, as an empty file returns successfully on execution.
On zsh, the same command returns
zsh: exec format error: ./true
on stderr and
126
for the echo statement.
This holds true when running zsh in sh compatibility mode:
ARGV0=sh zsh
I don't consider this of pressing importance, but it would be one step
closer to sh compatibility.